Two-terminal switching device using a composite material of nanoscopic particles and carbon nanotubes

ABSTRACT

An improved switching material for forming a composite article over a substrate is disclosed. A first volume of nanotubes is combined with a second volume of nanoscopic particles in a predefined ration relative to the first volume of nanotubes to form a mixture. This mixture can then be deposited over a substrate as a relatively thick composite article via a spin coating process. The composite article may possess improved switching properties over that of a nanotube-only switching article. A method for forming substantially uniform nanoscopic particles of carbon, which contains one or more allotropes of carbon, is also disclosed.

PRIORITY CLAIM

This application is a continuation patent application of U.S. patentapplication Ser. No. 14/051,697 filed Oct. 11, 2013 and entitled“Switching Materials Comprising Mixed Nanoscopic Particles and CarbonNanotubes and Methods of Making and Using the Same,” which claims thebenefit of U.S. patent application Ser. No. 13/074,792 filed Mar. 30,2011 and entitled “Switching Materials Comprising Mixed NanoscopicParticles and Carbon Nanotubes And Method Of Making And Using Same,”which claims the benefit of U.S. patent application Ser. No. 12/274,033filed Nov. 19, 2008 and entitled “Switching Materials Comprising MixedNanoscopic Particles And Carbon Nanotubes And Method Of Making And UsingSame,” the entire contents of each of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to a spin-coatable material and a methodfor manufacturing the same for use in the preparation of compositearticles and films. More particular, the present invention relates tosuch a material comprising a first volume of carbon nanotubes and asecond volume of nanoscopic particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to “Nonvolatile Nanotube Diodes andNonvolatile Nanotube Blocks and Systems Using Same and Methods of MakingSame,” (U.S. patent application Ser. No. 12/273,807), which isincorporated by reference herein in its entirety.

BACKGROUND

Any discussion of the related art throughout this specification shouldin no way be considered as an admission that such art is widely known orforms part of the common general knowledge in the field.

Nanotube fabric layers (or films) are used within a plurality ofsemiconductor devices. For example, U.S. patent application Ser. No.11/835,856 to Bertin et al. teaches methods of using nanotube fabriclayers to realize nonvolatile devices such as, but not limited to, blockswitches, programmable resistive materials, and programmable logicdevices.

As described by Bertin et al., a volume of nanotube fabric can be placedinto at least two nonvolatile resistive states by passing electriccurrents through said fabric. These nonvolatile resistive states can beused to create, for example, but not limited to, switch elements whichbehave as nonvolatile memory cells (wherein, typically, two nominalresistive states are used), nonvolatile variable resistor dividers forprecision voltage supplies (wherein, typically, a pair of nanotubedevices, each with a plurality of nominal nonvolatile resistive states,are used), and nonvolatile programmable logic devices (wherein,typically, multiple nonvolatile nanotube switch elements are used).

U.S. Pat. No. 7,335,395 to Ward et al. describes methods of applying ananotube fabric layer on a substrate. Said methods include spin coating(wherein a solution of nanotubes is deposited on a substrate which isthen spun to evenly distribute said solution across the surface of saidsubstrate), spray coating (wherein a plurality of nanotube are suspendedwithin an aerosol solution which is then disbursed over a substrate),and in situ growth of nanotube fabric (wherein a thin catalyst layer isfirst deposited over a substrate and then used to form nanotubes).Further, U.S. Pat. No. 7,375,369 to Sen et al. teaches a nanotubesolution which is well suited for forming a nanotube fabric layer over asubstrate layer via a spin coating process.

Studies for improved nanotube fabric layer and methods for forming thesame are continuing.

SUMMARY OF THE DISCLOSURE

As such, there exists a need for an improved nanotube fabric layer overa substrate and method for manufacturing same. It would be advantageousif said method provided a manner of control over the volume density ofnanotubes within said nanotube fabric layer. It would also beadvantageous if said method enabled formation of a nanotube fabric layerof significant thickness within a minimum number of spin coat processes,and preferably within a single spin coat process.

The invention provides an improved nanotube fabric layer over asubstrate and a method for manufacturing the same.

In particular, the present invention provides a nanotube devicecomprising a first electrode, a second electrode, and a compositearticle deposed between said first electrode and said second electrode.The composite article includes a first volume of nanotubes and a secondvolume of nanoscopic particles in a predefined ratio relative to thefirst volume of nanotubes.

The nanotube block switch of the present invention is formed over asubstrate by first combining a first volume of nanotubes with a secondvolume of nanoscopic particles in a predefined ratio relative to thefirst volume of nanotubes to form a mixture material, and thereafterdepositing said mixture material over said substrate via a spin coatprocess. In certain embodiments, the mixture can be homogeneous. In someother embodiments, the mixture can be heterogeneous.

The present invention also provides a method of forming substantiallyuniform nanoscopic particles of amorphous carbon from a volume of carbonblack material. Said method entails reacting, in a first processingstep, said volume of carbon black material with an oxidizing agent toform a carbon slurry. Thereafter, in a second processing step, saidmethod entails removing metallic contaminants from said carbon slurryusing a solubilization process. Thereafter, in a third processing step,said method entails filtering said carbon slurry to remove solubilizedimpurities. Thereafter, in a fourth processing step, said method entailsincreasing the pH level of the carbon slurry to obtain a colloidalsystem. In certain embodiments, the colloidal system can be homogeneousand/or stable. And thereafter, in a fifth processing step, said methodentails further filtering said colloidal system to remove particleswhich fall above a predetermined volume threshold.

The present invention further provides a resistive material comprising afirst volume of nanotubes and a second volume of nanoscopic particles ina predefined ratio relative to the first volume of nanotubes.

The present invention further provides a method for forming a compositearticle over a substrate is provided. The method can include depositinga first volume of nanotubes over said substrate to form a layer ofnanotubes; and depositing a second volume of nanoscopic particles, in apredefined ratio relative to the first volume of nanotubes, on the layerof nanotubes. In certain embodiments, the second volume of nanoscopicparticles can be deposited using ion implantation or vapor deposition.

In one aspect of the invention, a first volume of nanotubes is combinedwith a second volume of nanoscopic particles in a predefined ratio toobtain a mixture. The is can then be applied to a substrate via a spincoat process. The amount of said first volume of nanotubes and saidsecond volume of nanoscopic particles (that is, the ratio of nanotubesto nanoscopic particles within the mixture) are selected such as toprovide a desired volume density of nanotubes within the mixture. Inthis way, a composite article with a desired nanotube volume density canbe realized.

In another aspect of the present invention, the nanotubes within thefirst volume of nanotubes are carbon nanotubes, such as single wallednanotubes.

In another aspect of the present invention, the second volume ofnanoscopic particles includes nanoscopic particles which are otherallotropes of carbon, including but not limited to, polyaromatichydrocarbons, graphite, carbon nanopowder, amorphous carbon, carbonblack, and diamond.

In another aspect of the present invention, the second volume ofnanoscopic particles includes nanoscopic particles which are siliconbased materials, including, but not limited to, silicon oxide (SiO₂) andsilicon nitride (Si₃N₄).

In another aspect of the present invention, the second volume ofnanoscopic particles includes nanoscopic particles which are multi-wallnanotubes (MWNTs).

In another aspect of the present invention, the nanotube volume densitywithin the composite article is optimized to the needs of a givenapplication or device.

Accordingly, it is the object of the present invention to provide animproved method for forming a composite article over a substrate.

It is also an object of the present invention that said method comprisecombining a first volume of nanotubes with a second volume of nanoscopicparticles in a predefined ratio such as to form a mixture which is wellsuited for use within a spin coat process.

It is further an object of the present invention that said methodprovide a method for applying a relatively thick composite article orfilm over a substrate within a minimum number of spin coat processes andpreferably within a single spin coat process.

Other features and advantages of the present invention will becomeapparent from the following description of the invention which isprovided below in relation to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a nanotube device comprising a composite articleformed with only carbon nanotubes;

FIG. 2 illustrates a fabrication process suitable for fabricating thenanotube device depicted in FIG. 1;

FIG. 3 illustrates a nanotube device comprising a composite articleformed in accordance with certain embodiments of the present invention;

FIG. 4 illustrates a fabrication process for a nanotube device inaccordance with certain embodiments of the present invention;

FIG. 5 illustrates a nanotube device in accordance with certainembodiments of the present invention wherein multi-wall nanotubes(MWNTs) are used as nanoscopic particles;

FIG. 6 illustrates a nonvolatile nanotube device in accordance withcertain embodiments of the present invention; and

FIG. 7 illustrates the improved switching behavior of the nonvolatilenanotube device of FIG. 6, in accordance with certain embodiments of thepresent invention.

DETAILED DESCRIPTION

FIG. 1 illustrates a conventional nanotube device (e.g., a block switch)which makes use of a nanotube fabric layer comprising only carbonnanotubes. In a first operation, a carbon nanotube fabric layer 130 isdeposited over a first electrode 110. The carbon nanotube fabric layer130 is comprised of a volume of carbon nanotubes 130 a formed into acohesive fabric or film through the deposition process (e.g., spincoating, spray coating, or in situ growth). In a second operation, asecond electrode 120 is deposited over the carbon nanotube fabric layer130.

In a typical fabrication process, the thickness of the carbon nanotubefabric layer 130 is set above a certain threshold such as to prevent thesecond electrode 120 from becoming electrically connected (shorted) tothe first electrode 110 (via the electrode material bleeding through thecarbon nanotube layer 130, for example). As such, a nanotube fabriclayer of significant thickness is often required.

FIG. 2 illustrates a conventional fabrication process suitable forrealizing the nanotube block switch depicted in FIG. 1.

In a first operation 200 a, a first volume of carbon nanotubes 230 a isdeposited over a first electrode element 210 via a spin coating processforming a first intermediate nanotube fabric layer 240 a as illustratedby structure 200 b.

In a second operation 200 c, a second volume of carbon nanotubes 230 bis deposited via a spin coating process over the first intermediatenanotube fabric layer 240 a forming a second intermediate nanotubefabric layer 240 b as illustrated by structure 200 d.

In a third operation 200 e, a third volume of carbon nanotubes isdeposited via a spin coating process over the second intermediatenanotube fabric layer 240 b forming a third intermediate nanotube fabriclayer 240 c as illustrated by structure 200 f.

In this way, a nanotube fabric layer 240 (the combination of the first,second, and third intermediate nanotube layers 240 a, 240 b, and 240 c)of a required thickness is formed over first electrode element 210. In afourth operation, a second electrode element 250 is deposited over thenanotube fabric layer 240 as illustrated by structure 200 g.

In its most basic form, certain embodiments of the present inventionprovide a resistive material that can be used within a plurality ofdifferent applications. Such applications include, but are not limitedto, display elements, solar panels, and semiconductor circuits. Forexample, certain embodiments of the present invention include aplurality of nanotube based switching devices, including, but notlimited to, block switches, programmable resistive materials, andprogrammable logic devices.

Furthermore, certain embodiments of the present invention provideresistive materials, including films and fabrics, with controlled anduniform nanotube densities, significantly reducing the cost and/orimproving the performance of applications using such materials.

FIG. 3 illustrates one exemplary device, such as a nanotube blockswitch, in accordance with certain embodiments of the present invention.The device, such as the nanotube block switch shown, includes acomposite article 330 containing a mixture of nanotubes 330 a andnanoscopic particles 330 b in a predefined ratio (said nanoscopicparticles 330 b depicted as circular elements within FIGS. 3 and 4 forclarity). It should be noted that although FIG. 3 depicts the nanoscopicparticles 330 b as the discrete phase and the nanotubes 330 a as thematrix phase, the morphology of the nanoscopic particles 330 b andnanotubes 330 a may be different. For example, in certain embodiments,the nanotubes 330 a may form the discrete phase and the nanoscopicparticles 330 b may form the matrix phase. In some other embodiments,the nanotubes 330 a and the nanoscopic particles 330 b can both forminterconnected matrix phases. The composite article 330 can act as aswitching material between a first electrode 310 and a second electrode320. The fabrication, function, and use of nanotube block switches isdiscussed in greater detail within U.S. patent application Ser. No.11/835,856 to Bertin et al., which is incorporated by reference hereinin its entirety.

The nanoscopic particles are purposefully introduced in a predefinedratio with respect to the nanotubes to control the composition and,consequently, physical, electrical, and thermal aspects of the resultingcomposite articles. Whereas in other contexts, nanoscopic particlesother than nanotubes might be viewed as undesirable impurities, in thecomposite article of the present invention, the nanoscopic particles area deliberately added component, introduced to achieve the desired deviceperformance, such as desired switching attributes. Indeed, thenanoscopic particles are selectively mixed with nanotubes to form acomposite article having a predefined volumetric ratio of nanoscopicparticles to nanotubes. The ratio may be pre-selected and tuned toensure, for example, the desired range of electrical switching orresistive states. The attributes of the nanoscopic particles—thematerial, the size, the uniformity of the particulate population, theshape of the nanoscopic particles, its interaction with the nanotubes,etc.—can all be specifically selected to further tune the desired devicecharacteristics (e.g., electrical switching or resistivecharacteristics) of the resultant composite article. Moreover, incertain instances, the attributes of the nanoscopic particles itself mayfurther dictate the predefined ratio of the nanoscopic particles andnanotubes. Regardless, in each case, the purposeful and deliberateaddition of nanoscopic particles can have the common effect of allowinginventors additional control in tuning and refining the characteristics(electrical, physical, thermal or otherwise) of the composite article.For example, addition of the nanoscopic particles in a predefined ratiowith the nanotubes may decrease the switching voltages of the compositearticle as compared to switches formed from pristine nanotubes.

The predefined ratio of the nanoscopic particles to the nanotubes can beany ratio selected by the manufacturer depending on the application,method of combination, or the composition of materials used in thedevice. For example, in certain applications, some suitable andnon-limiting predefined ratio of the nanoscopic particles to thenanotubes may be from about 1:1 (one part nanoscopic particles to aboutone part nanotubes) to about 1:10 (one part nanoscopic particles toabout ten part nanotubes). For example, some suitable and non-limitingpredefined ratio of the nanoscopic particles to the nanotubes may be1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10.

The nanoscopic particles 330 b can take a plurality of forms dependingon the needs of an application or structure in which the methods of thepresent invention are employed. The nanoscopic particles may bespherical, oblong, square, irregular, or any other shapes as would bereadily apparent to ordinary skill in the art. The nanoscopic particlesmay have at least one dimension that is in the nanometer size. Forexample, the nanoscopic particles may have at least one dimension whichis less than 100 nm, 50 nm, 40 nm, 30 nm, 25 nm, 20 nm, 10 nm, 5 nm, or1 nm. In certain embodiments, the nanoscopic particles may havedimensions that are acceptable in semiconductor fabrication facilities,such as a CMOS facility. In certain embodiments, the nanoscopicparticles may be individual atoms or ions.

The nanoscopic particle can interact covalently or non-covalently toanother nanoscopic material, for example, carbon nanotubes. In certainembodiments, the nanoscopic particles may be miscible with the nanotubesand form a continuous material around the nanotube. In some otherembodiments, the nanoscopic particles may be inert to the nanotubes andremain in the same form as initially introduced into the mixture andtherefore non-miscible. In yet some other embodiments, the nanoscopicparticles may be partially miscible with the nanotubes and form asemi-miscible mixture with the nanotubes. In certain embodiments, thenanoscopic particles may have the ability to alter the porosity betweenthe carbon nanotubes.

The nanscopic particles may be introduced to the composite articleeither before deposition on the substrate or after the nanotube isapplied to the substrate. In the first application, the nanoscopicparticles can be combined with the carbon nanotubes by introducing theminto the solution containing carbon nanotubes then depositing thecombined mixture onto the substrate. In the second application, thenanoscopic particles can be introduced, for example, by ionimplantation, vapor deposition, sputtering, or other methods known inthe art after first forming a nanotube layer on the substrate.

Furthermore, in certain embodiments, the choice of such nanoscopicparticles can include a material or materials that can be formed with auniform particle size. In certain applications, the choice of ananoscopic particle can include a material or materials which can befabricated as individual particles within certain dimensions. Forexample, an application may require a nanoscopic particle whereinindividual particles are not larger than some fraction of a devicefeature size.

In some other embodiments, the choice of such nanoscopic particles caninclude a material or materials which do not adversely affect theswitching operation (that is, the changing from one nominal nonvolatileresistive state to another) of the composite article. In fact, incertain embodiments, the nanoscopic particles 330 b may improveswitching operation by lowering the voltage needed for the compositearticle to change its resistance.

In some other embodiments, inorganic nanoparticles can be utilized. Forexample, silicon based materials (such as, but not limited to siliconoxide and silicon nitride) can be used for said nanoscopic particles 330b.

In some embodiments, one or more allotropes of carbon (such as, but notlimited to, diamond, graphite, graphene, fullerenes, amorphous carbon,carbon black, carbon nanopowder, carbon nanobuds, carbon nanorods,carbon nanofoam, lonsdaleite, linear acetylenic carbon, polyaromatichydrocarbons, and the like) can be used for said nanoscopic particles330 b.

In certain embodiments, nanoscopic particles 330 b can include a mixtureof different nanoscopic materials, such as any combination of nanoscopicparticles 330 b described above.

The nanoscopic particles 330 b can be obtained by numerous differentways. For example, carbon particles having of particles of substantiallyuniform volume can be obtained through the process described below.Methods for obtaining other desired nanoscopic materials 330 b will bereadily apparent to one of ordinary skilled in the art.

-   -   In a first processing step, reacting a volume of carbon black        material with an oxidizing agent (such as, but not limited to,        nitric acid) to form a carbon slurry in order to decrease the        size of carbon black particles and further remove any metallic        contaminants (via solubilization). The first processing step may        be aided by further introducing other acids, such as        hydrochloric acid.    -   In next processing step, filtering the carbon slurry formed in        the first process step at low pH (for example, but not limited        to, via cross-flow membranes) to remove any solubilized        impurities    -   In a next processing step, increasing pH level of the carbon        slurry to realize a homogeneous and stable colloidal system (in        some operations, a sonication process may be used to improve        homogeneity)    -   In a next processing step, filtering the realized homogeneous        and stable colloidal system through a train of filters to remove        any particles which could lead to defects in the spin coated        film (in some operations, for example, said system would be        passed through filters with pores as small as 10 nm or 5 nm or        other filters with the smallest pore size available)

As described in greater detail below, the resulting colloidal system ofprocessed carbon particles can then be combined with a carbon nanotubesolution at a ratio which will enable the generation of a film or fabriclayer which will comprise a desired volume density of carbon nanotubes.

FIG. 4 illustrates a nanotube block switch fabrication process inaccordance with certain embodiments of the present invention. A firstvolume 420 of nanotubes 420 a is combined with a second volume 410 ofnanoscopic particles 410 a to obtain a mixture 430. The mixture 430 canbe homogeneous or heterogeneous. One of ordinary skill in the art willreadily appreciate the various different ways the mixture 430 can beformed.

In certain embodiments, mixture 430 can be formed so that the mixture430 can be utilized in semiconductor fabrication facilities, such as inClass 100, 10, or 1 facilities (e.g., CMOS facilities). For example, themixture 430 can be substantially free of undesirable particulate andmetal impurities, such as being substantially free of particulateimpurities that are greater than 1000 nm, 500 nm, 400 nm, or even 300 nmin diameter. As another example, the nanotubes 420 a and nanoscopicparticles 410 a can be combined in a solvent that is acceptable for usein semiconductor facilities, such as an aqueous (e.g., highly purifiedwater) or non-aqueous solvents that are compatible with semiconductorfabrication processes.

In process step 400 a, the mixture 430 is deposited over a firstelectrode element 440 via a spin coating process to form compositearticle 450 (as illustrated by structure 400 b). The mixture 430 allowsfor the deposition of significantly thicker (as compared to prior artnanotube solutions) layers (or films) within a single spin coat processas compared to nanotube-only liquids. For example, thickness rangingfrom about a few to hundreds of nanometers may be possible through asingle coat. Some non-limiting example thicknesses that can be achieveinclude 1, 2, 2.5, 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, or200 nm. As such, a sufficiently thick composite article suitable for usewithin a plurality of nanotube block switching devices (such as, but notlimited to, block switches, programmable resistive materials, andprogrammable logic devices) can be realized in a minimum number of spincoat process steps. Further, in many applications, such a layer can berealized within a single spin coat process step, significantly reducingprocess time and cost.

Then, a second electrode element 460 is deposited over the compositearticle 450 as illustrated by structure 400 c.

FIG. 5 illustrates a nanotube block switch with a composite article 530formed via an alternate embodiment of the methods of the presentinvention. A first volume of single wall nanotubes (SWNTs) 530 a can becombined with a second volume of multi-wall nanotubes (MWNTs) 530 b toform a mixture. In certain embodiments, said second volume of MWNTs 530b can act as the nanoscopic particles while said first volume of SWNTs530 a are single walled carbon nanotubes.

Then, said mixture can be deposited over a first electrode 510 via aspin coating process to form composite article 530. The compositearticle 530 can have very low level metal contamination. For example,the composite article 530 may have less than 10¹⁸, 10 ¹⁶, 10 ¹⁵, 10 ¹⁴,10 ¹³, 10 ¹², 5×10¹¹, 1×10¹¹, 5×10¹⁰, or even less than 1×10¹⁰atoms/cm². Thereafter, a second electrode 520 can be deposited over thecomposite article 530.

It should be noted that while FIGS. 4 and 5 depict two exemplaryfabrication process in order to clearly illustrate the methods of thepresent invention, said methods are not limited to these exemplaryembodiments. Rather, one of ordinary skill in the art would readilyrecognize other methods for forming the desired nanotube devices. Forexample, the methods of the present invention are well suited to forminga relatively thick carbon nanotube films. However, the present inventionis not limited in this regard. Indeed, the methods of the presentinvention are applicable to a plurality of applications wherein aspecific volume density of carbon nanotubes is required within a carbonnanotube film, including, but not limited to, those applicationsemploying very thin films. Accordingly, one of ordinary skill in the artwould readily recognize the various different embodiments forfabrication the desired nanotube devices of interest.

EXAMPLE

FIG. 6 depicts a nonvolatile nanotube switch. As shown, cell structure8700 having cell 8705 comprises a composite article 8710 containingnanotubes and nanoscopic particles. The nanoscopic particles can includecarbon particles having substantially uniform volume as described above.The composite article 8750 has top/end contact 8765 and bottom 8730contact. The present cell select and control structure includesconductive plug 8710 connecting bottom contact 8730 to an N+ regionembedded in P-type substrate PSUB. In the present cross sectional viewword line WL1 is used as one portion of the cell select circuitry. Cell8705 may be integrated on a 1024 bit array for the purposes ofelectrical testing to evaluate electrical characteristics of thecomposite article 8750. In one or more embodiments, tests include SET toprogram the cell (write 1), RESET to erase the cell (write 0) and READto access the stored state of the cell. SET, RESET and READ functionsare known in the art and discussed in greater detail above in relationto 3-D cell structures employing nanotube articles.

FIG. 7 summarizes typical RESET and SET electrical parameters, accordingto one or more embodiments. Specifically, typical applied pulse rise andfall times, duration, voltages and currents are listed. Testing hasrevealed that in certain embodiments and switch structures, thecomposite article 8710 containing nanotubes and nanoscopic particlesenables a lower operating voltage than does the CNT-only materialcounterpart. For example, various embodiments of the nonvolatilenanotube switch functions at operating voltages less than or equal toapproximately 5.0V. As a point of comparison, various switchingstructures having CNT-only materials to form the carbon nanotubearticles typically function at operating voltages between approximately7.0 and 8.0V. Moreover, testing has suggested that the composite article8710 containing nanotubes and nanoscopic particles, when used in certainswitch configurations, may be faster in performing the SET function thana CNT-only material counterpart. In other words, the composite article8710 containing nanotubes and nanoscopic particles may, in certainembodiments, be programmable under shorter duration write 1 operations.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art. It ispreferred, therefore, that the present invention not be limited by thespecific disclosure herein.

What is claimed is:
 1. A two-terminal switching device comprising: afirst electrode; a second electrode; and a switching composite articledisposed between and in constant electrical communication with each ofsaid first electrode and said second electrode of said two terminalswitching device, wherein said composite article comprises a firstvolume of nanotubes and a second volume of nanoscopic particles in apredefined ratio relative to said first volume of nanotubes; wherein atleast one of said predefined ratio and said second volume of nanoscopicparticles are selected in order to improve the switching functionalityof said two-terminal switching device.
 2. The two-terminal switchingdevice of claim 1 wherein the nanotubes comprising said first volume aresubstantially all carbon nanotubes.
 3. The two-terminal switching deviceof claim 1 wherein said second volume of nanoscopic particles includesnanoscopic particles containing at least one allotrope of carbon.
 4. Thetwo-terminal switching device of claim 1 wherein said second volume ofnanoscopic particles includes silicon oxide particles.
 5. Thetwo-terminal switching device of claim 1 wherein said second volume ofnanoscopic particles includes silicon nitride particles.
 6. Thetwo-terminal switching device of claim 1 wherein said second volume ofnanoscopic particles includes multi-walled nanotubes.
 7. Thetwo-terminal switching device of claim 1 wherein substantially all ofsaid nanoscopic particles within said second volume fall within apredetermined volume tolerance.
 8. The two-terminal switching device ofclaim 1 wherein at least one of the magnitude of said first volume ofnanotubes and the magnitude of said second volume of nanoscopicparticles is selected to realize a desired volume density of nanotubeswithin said switching composite article.
 9. The two-terminal switchingdevice of claim 1, wherein said first volume of nanotubes form a matrixphase and said second volume of nanoscopic particles form a discretephase.
 10. The two-terminal switching device of claim 1, wherein saidsecond volume of nanoscopic particles form a matrix phase and said firstvolume of nanotubes form a discrete phase.
 11. The two-terminalswitching device of claim 1, wherein said first volume of nanotubes andsaid second volume of nanoscopic particles form interconnected matrixphases.
 12. The two-terminal switching device of claim 1, wherein saidcomposite article has less than about 10¹¹ metal atoms/cm².
 13. Thetwo-terminal switching device of claim 1 wherein said second volume ofnanoscopic particles includes atomic silicon.
 14. The two-terminalswitching device of claim 1 wherein said improved switching function isa reduced switching voltage.
 15. The two-terminal switching device ofclaim 1 wherein said improved switching function is a faster switchingtime.